1. Field of the Invention
The present invention relates to certain novel diazo pigments, to a method of their preparation, and to their application in the pigmentation of organic materials.
2. Description of the Prior Art
The demand for yellow pigments with a high tinctorial yield, having a high degree of purity of tone (brightness), a good fastness to light, and good resistance to organic solvents, has been increasing, particularly in the polychrome graphic industry.
Printing inks prepared with yellow pigments should display good rheological properties, even at high pigment concentrations, and prints prepared with them should be bright and transparent.
It is known that particularly valuable yellow pigments are those which show a greenish yellow hue, inasmuch as one of the basic uses of yellow pigments is in obtaining, in admixture with blue pigments, green colors. Yellow pigments having a greenish yellow hue, when admixed with blue pigments, give green colors that tend to be both purer and brighter.
The need for yellow pigments to be of high tinctorial yield, good transparency, and of a satisfactory light fastness, has heretofore primarily been satisfied by the benzidine pigments. These pigments have, however, certain limits in various industrial applications because they show a high oil absorption, which tends to decrease the flowability of the pigments present in high concentration. Moreover, such pigments do not exhibit an altogether satisfactory transparency, which characteristic is very important in graphic polychrome printing.
In addition, benzidine pigments have the disadvantage that their preparation involves the handling and use of benzidine derivatives such as, for instance, 3,3'-dichloro-benzidine, which is highly toxic and requires very strict standards for handling and useage.